This invention pertains to coal liquefaction and hydrogenation processes to provide hydrocarbon gases and liquid product streams. More particularly, it pertains to a coal hydrogenation process wherein ground coal is segregated into an ash-reduced portion which is advantageously fed to a hydrogenation system and an ash-enriched portion which is gasified and utilized to produce the hydrogen needed in the hydrogenation system.
In the known processes for the liquefaction and hydrogenation of coal to produce useful hydrocarbon gas and liquid products, it is usually necessary to remove the very fine ash particles from the resulting liquid product stream in order for it to be commercially useful either as a fuel or as a hydrocarbon feedstock for further processing. The unconvertible solids in the feed to the high pressure liquefaction step require removal by the use of hydroclones to control their concentration in the liquefaction reaction. However, this liquid-solids separation step is a difficult and expensive procedure, requiring specialized equipment. Minimizing the solids to be removed will simplify this step, and eliminating the need for hydroclones would simplify the overall process. It is also recognized that considerable high purity hydrogen is required in coal liquefaction-hydrogenation processes. To produce this hydrogen, it has been proposed to gasify additional coal.
Coal cleaning processes, such as by washing, flotation, magnetic separation, etc., are generally known and used in the coal industry to remove dirt, rock and some ash from coal, either at the mine site or sometimes at coke producing plants. For example, U.S. Pat. No. 2,082,467 to Prins and U.S. Pat. No. 3,233,731 to Nailler disclose typical coal cleaning proprocesses using water washing and flotation to remove the coal portion containing high mineral matter or ash. U.S. Pat. No. 3,463,310 to Ergun discloses a typical coal cleaning process using magnetic separation to remove pyrites. Such coal cleaning processes are usually operated so as to remove as little of the coal as possible along with the undesirable materials which are discarded.
U.S. Pat. No. 3,926,775 to Schroeder discloses a coal hydrogenation process wherein the coal is water washed and separated into low and high ash fractions, with the low ash fraction being used in a hydrogenation process and the high ash fraction being burned in a steam power plant. But apparently no coal hydrogenation process has heretofore been proposed which would effectively utilize the ash-enriched coal fraction from a coal cleaning process and allow a relatively large portion of coal to be removed from the raw coal along with the ash-enriched fraction and then gasified to produce the hydrogen needed in a liquefaction-hydrogenation system, to which the ash-reduced fraction is fed.